USA : Debris points to lost lake sites

Many of us assume that the shape of our coastlines is more or less a constant feature of geography.

We all accept that the occasional severe storm might result in the loss of some shorefront property, but surely these changes are insignificant when considered on a continental scale.

Actually, a variety of climatological and geological processes have, over the millennia, altered America's coasts in fairly significant ways.

The Third Coast is no exception.

The Ice Ages brought dramatic changes to the Great Lakes, with lake levels rising and falling as the ice sheets alternately advanced and melted. About 10,300 years ago, Lake Erie was about 115 feet shallower than its current level, leaving more than half of the basin exposed as lush wetlands.

Because such environments were smorgasbords for hunters and gatherers, thousands of archaeological sites dating to this period must be submerged beneath the modern lakes. Finding and eventually exploring these sites represents a major challenge for archaeologists.

Geoarchaeologist Elizabeth Sonnenburg and her colleagues at McMaster University in Hamilton, Ontario, are developing a new method for discovering the traces of ancient American Indian activity on submerged landscapes. They are extracting 3-inch-diameter cores from lake-bottom sediments and carefully sieving the layers in search of microdebitage.

Microdebitage represents the tiniest byproducts of manufactured stone tools. These small bits of worked stone are smaller than 1 millimeter long. These byproducts might be small, but they are abundant on archaeological sites.

According to one estimate, more than 1 million pieces of microdebitage are created in the process of making a single stone tool. This means that most Stone Age sites should be carpeted with microdebitage.

If you had to depend on finding a large stone tool in a soil core, it would be highly unlikely that you would find very many sites. By focusing on the nearly ubiquitous and ridiculously abundant microdebitage, however, you have a much better shot at it.

Sonnenburg and her team searched the waters of Rice Lake north of Lake Ontario in Canada for traces of submerged archaeological sites. They chose a likely area just offshore from a known site and extracted five cores from the bottom of the relatively shallow water.

They recovered a total of 155 fragments of quartz microdebitage from three of the five cores. The fact that the tiny flakes are quartz rather than flint means the tool-makers were using the locally available raw materials rather than the harder to obtain flint.

The researchers noted in their article, published this month in the journal Geology, that quartz and quartzite were favored materials at many of the earliest sites in Ontario.

They speculate that the microdebitage recovered from the cores might represent "remnants of tools manufactured or sharpened on the spot during a hunting-gathering foray, as quartzite cobbles were readily available in the area."

This study demonstrates the great potential of microdebitage analysis for discovering submerged archaeological sites. Such techniques will allow us to recover important evidence of how ancient humans lived along their coastlines, which were, after all, not always the same as ours.